Test of PRISMA in Gas Filled ModeB.Guiot for PRISMA collaboration

INFN – Laboratori Nazionali di Legnaro

Measurements of small fusion cross sections are experimentally challenging

Motivation

C.L. Jiang et al., Phys. Rev. Lett. 89 052701 (2002) : 60Ni+89Y

C.L. Jiang et al., Phys. Rev. Lett. 93 012701 (2004) : 64Ni+64Ni

Example: the hindrance phenomenon

Principles of operation of a gas-filled magnetic spectrometer

Charge states merge

qmvB

vZq

to a first approximation, B does not depend on v

vacuum gas

Poor resolution (no single mass resolution) Basically a high-efficiency separator Typically operated at 0° for the detection of fusion evaporation residues

Problems with magnetic rigidity

Magnetic rigidity

0,5

0,7

0,9

1,1

1,3

1,5

1,7

1,9

0,01 0,10 1,00 10,00E/A (MeV/amu)

B

(Tm

)

58Ni

112Sn

148Sm

176Hf

208Pb

252Fm

<q> according to Betz

The average charge state can be very low in gas for a slow, heavy ion

for a central trajectory Prisma is limited to A<180

By using non-central trajectory we can reach B=1.5Tm

TmB 2.1

Prisma max. rigidity for central trajectory

Magnetic rigidity of Evaporation Residues

Projectile and ER rigidity as a function of the target Z @ E=VB

for all practical cases

ERBEAM BB

Forget reverse kinematics!

S

Ni Ca

Se

1.5Tm

projectileCN

3230 mm

800 mm

EFB

EFB

GFM operation of Prisma. General considerations

the drift-chamber + detectors can move back 70cm and more

Drift chamber not to be operated in gas: • mult.scattering with no focusing elements• cannot optimize gas pressure in magnets

Gas filling: 4He is the most popularbut other gases should be tested

detector

C-foil window

Gate valve

Gas filling

EFB

EFB

1.2Tm

The setup for the GFM operation of Prisma

Prisma at 0°

1.5TmDRIFT

Detector chamber

C-foil window50g/cm2

beam dump

detector

shifted 30cm

new chamberfor GFM det.

Si strip detectors for the gas-filled mode operation

Junction sideJunction side

Matrix of 2 x 3 Si detectorsMatrix of 2 x 3 Si detectorsThickness Thickness ~~ 300 300 mmActive area = 5 x 5 cmActive area = 5 x 5 cm22, 16 resistive strips, 16 resistive strips

Ohmic sideOhmic side

3 mm3 mm

Electronics scheme

100100

PA

PA

PA

A

A

A

ADC

Discr

Discr

Discr

Bit

Patt

ern

PA ADC

A EnergyEnergy

X Pos. X Pos.

Y Pos. Y Pos.

CFD

TDC

Beam referenceBeam reference

TriggerTriggerDelay = 100 nsDelay = 100 ns

Home made Electronics(PAs and shaping amplifiers)INFN NAPOLI

Summary and program

Test of electronics

Test of C-foil window with different gases

In beam test :

Pre-amplifiers: crosstalk

Preliminary tests with Si and α-source : signals OK

58Ni (200 MeV) + 197Au , PRISMA @ 60° : end of june

PRISMA in GFM : adequate Bρ up to masses A~200

Focal plane detector : 6 Si strips detectors 10 × 15 cm2

Aim : fusion reactions studies ; no super heavy elements

Under progress

Windows from GSI and LNL

Test of spot size, transmission, beam separation vs energy and gas…

Under progress

ANAMARI CodeANAMARI Code

0,0

5,0

10,0

15,0

20,0

0,0 0,2 0,4 0,6 0,8BQ

fwhm

(cm

)

40Ca+172Dy 1Torr

X

Y0

5

10

15

20

25

0 0,2 0,4 0,6 0,8

BQ

fwhm

(cm

)

32S+184W 1Torr

Y

X

•65cm•100cm•150cm•200cm

Section by section calculation using mid-section energy and <q> via 1st order transfer matrix Straggling added at the end of each section (assuming gaussian distribution ) Charge exchange not taken into account (ok if mean free path is short) Very fast

Without charge exchangeone cannot optimize the pressure one cannot estimate the background

being implemented

48Ca (200MeV) + 172Yb 216Th + 4n

1Torr He

216Th

48Ca

ANAMARI CodeANAMARI Code

The program assumes a full charge state equilibration. As we will see, it may not be appropriate

TRAJIG CodeTRAJIG Code

0,0

5,0

10,0

15,0

20,0

25,0

30,0

35,0

0,0 0,2 0,4 0,6 0,8 1,0BQ(T)

fwhm

(cm

)

0,0

5,0

10,0

15,0

20,0

25,0

30,0

0,0 0,2 0,4 0,6 0,8 1,0

BQ(T)

fwhm

(cm

)

48Ca (200MeV) +172Yb 216Th + 4n

1Torr

36S (160MeV) +184W 216Th + 4n

1Torr

65cm100cm150cm200cm

X

Y

4th order Runge-Kutta trajectory calculations Straggling added step by step, according to G.Amsel, G.Battistig, A.L’Hoir Nuc. Instr.

Methods B201 (2003) 325 Charge exchange included. Cross sections from A.S.Schlachter et al. Phys.Rev. A11

(1983) 3372 assuming detailed balance and 1e exchange approximation. Yields reasonable results from high vacuum to large pressures

above: first calculations without charge exchange

TRAJIG CodeTRAJIG Code

Approximations usedApproximations used: :

• schematic (ideal) optical elements (no fringing field) • cross sections and charge distributions are calculated only once per section, at the average estimated energy.

The charge-exchange cross sections are estimated by • single electron loss or capture approximation plus ...• empirical adjustment in order to reproduce the assumed charge distribution

The most critical approximations are related to the charge-exchange

charge distribution: R.O.Sayer, Revue Phys. Appl. 12, 1977, 1543.

cross sections: A.S.Schlachter et al. Phys.Rev. A11 (1983) 3372

Trajig calculation for AuMeVNi 19758 )220( @60° 0° aperture gas: Helium

197Au

10-5 mb

10-4 mb

10-2 mb

0.1 mb

0.2 mb

0.5 mb

1 mb

2 mb

5 mb

10 mb

197Au

0

5

10

15

20

25

30

35

40

0,01 0,1 1 10

P(mbar)

fwhm

(cm

)

Trajig calculation for AuMeVNi 19758 )220( @60° 0° aperture gas: Helium

charge-exchange contribution

multiple scattering contribution

Trajig calculation for AuMeVNi 19758 )220( @60°

58Ni 197Au

0° aperture

0.01mb

0.1mb

0.5mb

1 mb

2 mb

3 mb

5 mb

Trajig calculation for AuMeVNi 19758 )220( @60°

58Ni 197Au

3° aperture

0.01mb

0.1mb

0.5mb

1 mb

2 mb

3 mb

5 mb58Ni 197Au

Calculated 2D XY spectrumCalculated 2D XY spectrum

197Au58Ni

Focal plane detector

2 mbar of He

AuMeVNi 19758 )220( Prisma @ 60° 3° aperture

Trajig calculation AuMeVNi 19758 )220( @60° 0° aperture

0.01mb

0.1mb

0.5mb

1 mb

2 mb

3 mb

5 mb58Ni 197Au

gas: Argon

48Ca (200MeV) + 172Yb 216Ra + 2p2n

216Ra

172Yb

48Cano charge exchange2mb He

with charge exchange

A fusion example

2mb Ar

ER

48Ca

48Ca (200MeV) + 172Yb 216Ra + 2p2n

10mb He

ER

48Ca

other options

How does GFM Prisma compare? How does GFM Prisma compare?

Sep. Laboratory Configuration Main topic

RITU JYFL QDQQ HE spect. Z<103

GARIS RIKEN DQQD SHE prod. & chem.

DGFRS FLNR DQQ SHE production

BGS LBL QDD SHE prod. & chem.

TASCA GSI DQQ SHE prod. React. & Chem.SHE spectr. Z>104

PRISMA LNL QD H.I. fusion reaction ?

• we cannot get into the SHE competition (accelerator and rigidity limitation) • we are ill equipped to compete in the HE spectroscopy (not with GFM) • a possibility is fusion reaction studies: it depends strongly on beam rejection, necessary to measure at low cross sections and reliability of the simulations.